1. Field of the Invention
The present invention relates to a reactant gas humidification apparatus and a reactant gas humidification method in which a reactant gas is supplied to one surface of a water permeable membrane, and a humidifying fluid is supplied to the other surface of the water permeable membrane for humidifying the reactant gas.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a membrane electrode assembly (MEA) which includes two electrodes (anode and cathode), and an electrolyte membrane interposed between the electrodes. The electrolyte membrane is a polymer ion exchange membrane. The membrane electrode assembly is interposed between a pair of separators. The membrane electrode assembly and the separators make up a power generation cell for generating electricity. In use, a plurality of the power generation cells are stacked together to form a fuel cell stack.
In the fuel cell, a fuel gas such as a gas chiefly containing hydrogen (hereinafter also referred to as the “hydrogen-containing gas”) is supplied to the anode. A gas chiefly containing oxygen or the air (hereinafter also referred to as the “oxygen-containing gas”) is supplied to the cathode. The catalyst of the anode induces a chemical reaction of the fuel gas to split the hydrogen molecule into hydrogen ions and electrons. The hydrogen ions move toward the cathode through the electrolyte membrane, and the electrons flow through an external circuit to the cathode, creating a DC electrical energy.
In the fuel cell, in order to achieve the efficient power generation performance, it is necessary to maintain the suitable humidified state of the electrolyte membrane. For this purpose, in the known technique, a humidification apparatus is provided for humidifying the fuel gas or the oxygen-containing gas in advance using water, and the humidification apparatus is connected to the fuel cell for supplying the humidified fuel gas or the oxygen-containing gas to the fuel cell.
For example, Japanese Laid-Open Patent Publication No. 2003-187839 discloses a fuel cell humidification apparatus as shown in FIG. 21. According to the disclosure, a humidification membrane 1 is interposed between a pair of resin plate members 2. A plurality of the resin plate members 2 and the humidification membranes 1 are stacked together to form a stack. A humidification outbound flow field 3 for the air supplied to the air electrode of the fuel cell is provided between one surface of the humidification membrane 1 and one of the plate members 2, and a humidification inbound flow field 4 for the off gas discharged from the air electrode of the fuel cell after reaction is provided between the other surface of the humidification membrane 1 and the other plate member 2.
However, in the humidification apparatus, since the air before reaction is supplied to the humidification outbound flow field 3 on one surface of the humidification membrane 1, and the off gas is supplied to the humidification inbound flow field 4 on the other surface of the humidification membrane 1, humidification of the air before reaction by the off gas is only carried out near the humidification membrane 1. Therefore, it is not possible to efficiently humidify the entire air before reaction flowing through the humidification outbound flow field 3 by the water in the off gas flowing through the humidification inbound flow field 4.
In the technique, in order to achieve sufficient humidification of the air before reaction, the overall size of the humidification apparatus needs to be significantly large. Thus, a large space is required for installation of the humidification apparatus. For example, it is not possible to mount the large humidification apparatus in a vehicle.
Further, in the humidification apparatus, a plurality of plate members 2 and humidification membranes 1 are stacked together, and an outbound passage for supplying the air to each of the humidification outbound flow fields 3 and an inbound passage for supplying the off gas to each of the humidification inbound flow fields 4 extend through the stack of the plate members 2 and the humidification membranes 1 in the stacking direction. In the structure, seal members are provided around the outbound passage and the inbound passage for preventing leakage of the air or the off gas.
In order to achieve improvement in the humidification efficiency, for example, in some applications, each of the humidification outbound flow field 3 and the humidification inbound flow field 4 includes a plurality of serpentine flow grooves or the like. Thus, when two plate members 2 are provided such that the humidification membrane 1 is interposed between the plate members 2, the flow grooves of the humidification outbound flow field 3 and the flow grooves of the humidification outbound flow field 4 intersect with each other in some areas. As a result, for example, the seal member may be deformed downwardly by its weight into the flow grooves. Thus, the desired sealing performance cannot be maintained. Further, the rigidity in the stacking direction may be lowered disadvantageously.